The present invention relates to rotary regenerative heat exchangers and particularly to air preheaters for the transfer of heat from a flue gas stream to an incoming combustion air stream. The invention particularly relates to the structure and configuration of the heat transfer plates contained in such heat exchangers.
A rotary regenerative heat exchanger is employed to transfer heat from one hot gas stream, such as a hot flue gas stream, to another cold gas stream, such as combustion air. The rotor contains a mass of heat absorbent material which first rotates through a passageway for the hot gas stream where heat is absorbed by the heat absorbent material. As the rotor continues to turn, the heated absorbent material enters the passageway for the cold gas stream where the heat is transferred from the absorbent material to the cold gas stream.
In a typical rotary heat exchanger, such as a rotary regenerative air preheater, the cylindrical rotor is disposed on a horizontal or vertical central rotor post and divided into a plurality of sector-shaped compartments by a plurality of radial partitions, referred to as diaphragms, extending from the rotor post to the outer peripheral shell of the rotor. These sector-shaped compartments are loaded with modular heat exchange baskets which contain the mass of heat absorbent material commonly formed of stacked heat transfer plates. These heat transfer plates are closely stacked in spaced relationship to provide a plurality of passageways between adjacent plates for flowing the heat exchange fluids therebetween.
In order to maintain the plates in the spaced relationship, a whole variety of devices or configurations have been proposed in the past. One such configuration is disclosed in U.S. Pat. No. 2,558,752 wherein the plates are provided with tabs punched and bent from the plates to form spacers. Although this is a viable means for stacking and spacing the plates, and although they exhibit favorable heat transfer rates, the results can vary widely depending on the specific design and the tab dimensions. Also, factors other than thermal performance are important such as the structural rigidity, the pressure drop and cost factors such as the volume and weight of the plates necessary for a certain level of performance.
An object of the present invention is to provide improved heat transfer means for rotary regenerative heat exchangers and particularly to improved means for spacing heat transfer plates in such heat exchangers to optimize performance and reduce costs. In accordance with the invention, the heat transfer plates have spacer tabs punched and bent outwardly from the plates arranged in parallel rows wherein the tabs have specific ranges and ratios of dimensions to optimize the thermal performance, provide structural rigidity and reduce the cost, weight and volume.